Two pack Hull coating

[Troyboy]

2 hours ago, Hudds Lad said:

i love those baseplate blacking arguments on facebook, never takes long for the first armchair metallurgist to state that steel requires oxygen to rust and there is no oxygen down there so the baseplate cannot rust  

We all know the real reason boatyards don't black the baseplate is most yards cannot get the boats high enough to be able to get underneath . 

[LadyG]

On 27/04/2021 at 09:34, Hudds Lad said:

i love those baseplate blacking arguments on facebook, never takes long for the first armchair metallurgist to state that steel requires oxygen to rust and there is no oxygen down there so the baseplate cannot rust  

If there is  no oxygen there would be no fish. 

Edited April 30, 2021 by LadyG

[bizzard]

H2 oh

Edited April 30, 2021 by bizzard

[blackrose]

I think there's some misunderstanding here. Firstly fish breath dissolved oxygen rather than the molecular oxygen bound up in H2O.

 

Secondly people on both sides of this argument are guilty of absolutism and science is not about absolutes. There's a gradient of dissolved oxygen in a water column which will be greater at the top than at the bottom. So it follows that although mild steel corrosion will be more prevalent at the top of the water column it can also occur at the bottom, but much more slowly.

 

So it really boils down to whether at 2 - 3ft down in fresh water there is enough dissolved oxygen to worry about corrosion of a 6 -10mm baseplate. That should form the basis of any discussion on the subject.

Edited April 30, 2021 by blackrose

[Mudskipper]

3Fe + 4H₂O = Fe₃O₄ + 4H₂    [ H₂O being water and Fe₃O₄ being Iron Oxide, aka RUST ]  Fish breathe dissolved oxygen.  Dissolved oxygen is the same principle of as dissolving an asprin - it is a suspension and the composition of the water molecules is unchanged.  Fish gills extract dissolved oxygen, passing the oxygen through microscopic holes into the bloodstream in the same fundamental way as lungs do for mammals.  The process of changing iron to iron oxide, on the other hand, is a chemical reaction and therefore involves the alteration of molecules.  That baseplate definitely looks rusty.  The carrying companies did not tip the boats over on their sides and black the bottoms for the fun of it. 

[blackrose]

1 hour ago, Mudskipper said:

 That baseplate definitely looks rusty.  The carrying companies did not tip the boats over on their sides and black the bottoms for the fun of it. 

 

So do the sides. They don't look like they've seen any paint for at least a decade. 

 

But I'm not sure where the idea often espoused on this forum comes from, that working boaters and carrying companies did everything correctly? The implication always seems to be that we should be trying to emulate them. The truth is that they knew about some things, but were often completely uneducated. We have far more knowledge on many more things including science & technology these days.

 

I'm afraid just because people in the past did something a certain way is not in itself a valid argument for continuing to do it. If it were we would still be sending children up chimneys!

Edited April 30, 2021 by blackrose

[Jackofalltrades]

5 minutes ago, blackrose said:

But I'm not sure where the idea often espoused on this forum comes from, that working boaters and carrying companies did everything correctly? The implication always seems to be that we should be trying to emulate them. The truth is that they knew about some things, but we have far more knowledge on many more things including science & technology these days.

 

But most people seem to have lost the knowledge that untreated steel immersed in water rusts.  Who knew?!  Still, I suppose it keeps the steelworkers in gainful employment.

 

[LadyG]

On 24/04/2021 at 16:56, haggis said:

I don't think so as the company has done a lot of research on this method of blacking and have been doing it for several years.  if it wasn't working  I think we would have heard about it and they wouldn't be so busy. However the proof will be when we go back in September to get the blacking done again but from what we can see it still looks good. 

 

Haggis

Yes, OK but I don't want to haul out every three years to recoat bitumen, the idea is to remove the small amount of bitumen, which presumably was used  because  it was available, cheaper and easier. I intend to restore the epoxy finish it had from new, which lasted twenty years. 

I am going to re coat with epoxy two pack. 

[Sea Dog]

35 minutes ago, Jackofalltrades said:

Still, I suppose it keeps the Chinese steelworkers in gainful employment.

Fixed that for you.

[Jackofalltrades]

3 minutes ago, Sea Dog said:

Fixed that for you.

Do they come over here and do overplating too?

[Sea Dog]

Just now, Jackofalltrades said:

Do they come over here and do overplating too?

It's only a matter of time...

 

[Jackofalltrades]

4 minutes ago, Sea Dog said:

It's only a matter of time...

 

In the meantime boatyards will be only too happy to quote for overplating work for boat owners who were led to believe baseplates don't rust and therefore don't need blacking...

[Sea Dog]

9 minutes ago, Jackofalltrades said:

In the meantime boatyards will be only too happy to quote for overplating work for boat owners who were led to believe baseplates don't rust and therefore don't need blacking...

Well, yes, but only if they can get the steel...from China.

[Jackofalltrades]

21 minutes ago, Sea Dog said:

Well, yes, but only if they can get the steel...from China.

 

* Other sources of steel are available.

 

But my point stands - boatyards (and builders) are only too happy to NOT black baseplates (probably because it's too much like hard work and not profitable enough) so they say it's "not needed" and just do the easy bits (the sides) until such time that overplating is needed and the five figure sum involved makes it worth their effort.

 

[Sea Dog]

1 hour ago, Jackofalltrades said:

 

* Other sources of steel are available.

 

But my point stands - boatyards (and builders) are only too happy to NOT black baseplates (probably because it's too much like hard work and not profitable enough) so they say it's "not needed" and just do the easy bits (the sides) until such time that overplating is needed and the five figure sum involved makes it worth their effort.

 

I'd certainly find it difficult to disprove your point Jack. I suspect lack of a definitive argument either way is largely responsible for most (including me) not going to the trouble of blacking the baseplate, particularly now the 10mm baseplate has become ubiquitous. Because it's such a challenge, the evidence of the requirement needs to be overwhelming doesn't it,  but I agree it doesn't make not blacking the bottom the right answer either.  I'd do mine if it was easy, but just conning the Long Haired Admiral into believing she enjoys doing the sides with me is hard enough!